Method of making cast iron and addition material therefor



Patented M ay'1 3, 1941 UNITED STATES PATENT OFFICE METHOD OF MAKINGCAST- IRON AND ADDITION MATERIAL THEREFOR Thomas E. Barlow, Columbus,Ohio, assignor to Battelle Memorial Institute, Columbus, Ohio,

corporation of Ohio No Drawing. Application March 24; 1939,

Serial Nonsense 2 Claims.

lacy type of graphite is frequently associated with patches of ferrite,commonly referred to as snowballs or primary ferri to differentiate fromthe ferrite which is normally found in certain compositions. Althoughmodified or dendritic cast iron is said to have certain uses such as inthe manufacture of heat resistant castings, it

- is found to exhibit lower tensile and transverse;

strength, lower deflection, lower resilience, decreased wear resistanceand greater tendency to chill than the so-called normal irons. For thesereasons the modifi structure is deemed to be unsuited to the majority ofthe uses of cast-iron. There are a number of alloys on the market todaywhich will, to some extent, eliminate the tendency of gray iron tomodify. One of the most common of these and the one on which the mostwork has been done is ferrosilicon. Unfortunately, however, the use offerrosilicon is accompanied by a tendency towards shrinkage,

' blow-holes and porosity. T0 obtainmaximum effects from ferrosilicon,it is frequently necessary to add as much as 1.50 per cent silicon totheladle. When adding more than 1.00 per cent silicon the tendency to formblow-holes and shrinks becomes increasingly pronounced. With 1.5 percent' silicon or more added to the ladle, it is almost impossible tocast completely sound test bars in green sand. The amount offerrosilicon which may be used without danger of promoting porosityv andlow strength is frequently insufficient to offset the tendency of theiron to modify. This is especially true of superheated irons.

Various other alloys have been used as ladle additions for the purposeof preventing modification of cast iron with some success. An alloy oftitanium, aluminum, silicon and iron has been somewhat successful buttheindications are that it is unduly concentrated to enable it to obtainthe best results. The addition of more than 3 ounces of this alloy perhundred pounds of iron seems to be actually harmful.

Calcium silicide has been used as a ladle addition to prevent themodification of the cast iron. However, the fumes ensuing from its useare rather objectionable and there is room for improvement in' theresults attainable therewith.

Silicon carbide is somewhat successful for the purpose in question.However, the increase in carbon and silicon resulting from its use tendsto offset the beneficial effects thereof.

It has been found that the use of pure aluminum in the foundry for thepurpose of preventing modification of cast iron is not advantageous.Apparently, the aluminum accumulates during melting and causes pin-holesand blowholes. Also, the aluminum is so potent as a ladle addition thatthe slightest excess causes these same casting defects. -It is claimedthat if the ladle addition alloy contains-twice as much silicon asaluminum, the two elements flux ofi as a low melting point slag and thatthis prevents the aluminum content from building up to the danger point.I However, even the combination of silicon and aluminum in theproportions indicated for the production of an alloy to be used inpreventing modification of the cast iron leaves something to be desired.I

One of the objects of this invention is to provide a method and an alloyfor use therein which will relieve the above-mentioned modifiedstructural deficiencies of the graphite-in the iron.

Another object of this invention is to produce an alloy for the purposeindicated which will be intrinsically beneficial to the physical andmechanical properties of the cast iron, instead of being detrimental orneutral in its effect upo such physical and mechanical properties. pThis invention consists in the conception and verification of the-factthat a method of making cast iron can be greatly improved by introducingin'to the cast iron, while it is in molten form, a copper base alloywhich preferably contains aluminum and silicon and which may also con-'tain manganese. It has been found that the in- .troductionof such analloy intoiahe molten cast iron is. far superior to the effects of anyof its components when they are added separately. The effect of such asingle alloy as an addition material for the cast iron is also superiorto the combined effects of all its components when they are added asferrosilicon, ferromanganese, copper shot'and aluminum wire, forexample. The superiority is apparently at least, partly due to (1)- thesuperior distribution of the individual elements when added as a singlealloy and (2) the low melting point of the alloy which is approximately1500 F. When my alloy is added to cast iron, it not only relieves oreliminates the abovementioned modified structural conditions of thegraphite in the iron but it also introduces an alloying element orelements intrinsically beneficial rather, than detrimental or neutral tothe improvement of the physical and mechanical properties of the castIron.

Copper was decided upon 'as a base for the alloy for three reasons. Inthe first place, tests have shown that copper in itself has a tendencyto relieve the modified condition referred to above. Secondly, copperimparts definite benefits to cast iron, especially in regard toincreasing density, decreasing chill, decreasing section sensitivity,increasing machinability and increasing strength and toughness. Also,large additions of copper do not tend to cause foundry defects such asblow-holes, pin-holes, shrinks, etc. In the third place, copper is a lowpriced metal and is readily available.

Aluminum was chosen as the chief deoxidizing element. It was felt, andlater proved, that no harmful effects would result from the use ofaluminum when diluted with a large amount of other elements such ascopper. Also, when diluted with copper, no difilculty was had in gettinguniform distributionof the aluminum in the molten cast iron bath.Another point of some consequence is the fact that a. small amount ofaluminum is said to produce better distribution of copper in cast iron.

One undesirable feature of aluminum additions to cast iron is the factthat a finely divided oxide is formed which is frequently difficult toseparate from the molten cast iron. These oxide particles frequentlycause foundry defects. For thi reason, silicon is added to the alloyand, as indicated, manganese may also be added. When the correct ratioof silicon or of silicon and the manganese to aluminum is present, a lowmelting point slag is formed which readily separates from the moltenmetal. In addition, both silicon and manganese have a beneficial effectin regard to elimination of dendritic graphite.- In no case is itnecessary to maintain the silicon and manganese contents of the alloy sohigh as to introduce any weakening effect into the resulting cast iron.In fact, the addition of manganese, especially in the presence ofcopper, is known to strengthen rather than weaken cast iron.

The range ofcomposition which is best suited for the aluminum, silicon,copper alloys is as follows:

. Percent Aluminum 1 to Silicon 6 to Copper 50-to 93 iron may be presentpercentages up to 30%.

.However, dilution of this alloy with iron would necessitate a largeraddition of the alloy to the molten cast iron and'is therefore notdesirable. The cost of producing-the alloy can be materially lowered byintroducing the silicon'and manganese as ferrosilicon andferromanganeseithereby introducing some iron. A150,; ironis a'commonimpurity in many of the materiais'of manufacture. However, the bestresults can be .obtained by maintaining the iron content below 10%.

sufficient to-oifset any ordinary tendency of the iron to modify. It isdesirable to have the alloy sufliciently dilute to require 1% so as totake advantage of the apparent mass action effect involved. and also toensure better distribution of the more powerfully deoxidizing elementspresent .such as aluminum and silicon. However, it is not advisable tohave'the alloy so dilute that more than 1% is required because of thereduction of metal temperature effected by large ladle additions. 1 Dueto the low melting point of the alloy, '1% can be added with nodifficulty and still permit the addition of ferrochromium,ferromolybdenum, ferrovanadium, nickel, copper and other alloys whichare frequently added for special purposes. In unusual cases, where alarge degree of modification is encountered or where it is desirable toadd more copper for special purposes, up to 2% of the alloy can be addedwithoutexcessive chilling of fairly hot molten iron. It has been foundthat this alloy unlike other deoxidizers such as silicon and aluminum,is not detrimental when added in excess of the recommended amount.

Aluminum contents of less than 1% would not be sufficient for efiicientdeoxidation. Over 10% aluminum in the alloy would tend to introduce anexcessive amount of aluminum into the resulting cast iron. Also testshave shown that aluminum contents over. 6% are decreasingly effectiveand therefore uneconomical after exceeding 10%.

The silicon-content of the alloy should be at least twice that of thealuminum and-at least 6% in order that the aluminum and silicon oxidesformed will make a fusible slag which will separate readily from themolten metal; .Also it was found that if the silicon content was 10% orgreater, the resulting alloy became extremely friable. This is a verydesirable feature in that it permits low cost crushing of the materialwhich will permit the production of the alloy at a. lower cost thanwould be possible if shotting we're necessary. Also, many authoritiesare of the opinion that a crushed alloy is more desirable due to thesmall sizes that may be available. The rate of solution will thereforebe more rapid since the ratio of surface to mass is larger. The upperthe fact that it is merely a diluent. Thus, the

limit of 25% silicon is based on the fact that a higher percentage wouldintroduce a detrimental amount of silicon into the resulting cast iron.The. optimum percentage of silicon in the alloy is between 10% and 15%.

The manganese content of the alloy can be varied over a fairly widerange, though of course manganese is not absolutely essential andtherefore may be absent. It has a beneficial effect both m increasingthe effectiveness of the lower aluminum content alloy and also inlowering the final cost of the alley. Manganese is also very helpful informing a low melting point slag which readily separates from the molteniron. It appears that a very low manganese alloy or even a manganesefree alloy will have a considerable degree of the beneficial efiects ofthese alloys. More than 25% manganese is not advisable because it wouldraise the final manganese content of the resulting cast ironexcessively. Although an, increase in the manganese content of the castiron acts as a strengthener, the buyers of cast iron frequently set verydefinite limits on the manganese range.

Any alloy which would tend to raise the manganese content to a markeddegree, would, of course, increase the difllculty of maintaining a fixedmanganese content in the'cast iron. In some cases it would be. necessaryto keep the manganese content of the alloy to a minimum. The

optimum amount of manganese in the alloy is believed to be approximately10%, although up to 25% may be used.

The percentage of copper in the above alloy should be as high aspossible due to its beneficial efiect both as a strengthener andtoughener of 'cast iron and also as regard its effect on reduction ofchill and section sensitivity and on increasing the machinability.Copper provides, (1) a base to carry the deoxidizing" element and theslag forming elements, (2) a means of introducing a large amount ofalloy to the cast iron withoutcausing foundry defects, and (3)introduces beneficial effects other than those obtained from otherfoundry defects that frequently accompany ladle additions of highmelting point alloys. Even if comparable results could be obtained fromthe independent additions of aluminum,

ferrosillcon, ferromanganese and copper to the ladle, the low meltingpoint of the combined alloy would be an entirely justifiable reason forusing it in preference to the separate components.

In the development of my invention, four different alloys were made in asmall induction electric furnace lined with a clay graphite crucible.The melting practice was as follows: ,Ferrosilicon and ferromanganesewere placed in the bottom of the furnace and covered with copper shot.When this charge was completely molten, the power was shut off, andaluminum was added in the form of wire. The resulting alloy was pouredinto small dry sand pig molds. In every case the alloy was crushed topass a 6 mesh screen and was retained on a 28-mesh screen. The alloyswere designated as follows:

'Alloy 1:

Percent Aluminum 3 Silicon 9.5 Iron 0.5 Copper 87 Alloy 2:

' Percent Aluminum 3 Y Silirnn 9,5

Manganese; 10 Iron 2.5

' Copper '75 Alloy 3:

Percent Aluminum 6 Silirrm 12 Ir 2 Copper 80 Alloy 4:

. Percent Aluminum 6 Silicon 13 Manganese r 10.5 Ir 2.5 Copper 68 Castiron melts were made in an 120 lb'. induction electric furnace linedwith a magnesia crucible. The charge for each heat was essentially thesameand consisted of pig iron, scrap steel, ferromanganese, ferrosulfideand ferrosilicon. The ferro alloys were added to the charge beforemelting was complete. Three-40 lb. ladles were poured from each 120 lb.heat. Each ladle of iron was treated with the desired ladle addition asindicated in the following tables. The ladle addition was made to thestream of metal while transferring the metal from the furnace to theladle. The molten iron'was allowed to cool to 2550 F. before pouringinto green sand molds.

areas under the transverse strength-deflectioncurves were used as ameasure of resilience.

All values shown in the following tables are the average of four tests.

Averoge'physical properties of cast irons inoculated with ferrosilicon.copper and ferrosilicon, and aluminum-silicon-copper alloy 1 I Trans.Brinell Max. Trans. Resih- Bar No. temp Ladle addition load deg ence- T.S. 13 rs;- C. Si Cu F. Pounds Inches [n.Jbs. Lira/in. I Pct. Pct. Pct.

2550 .045#I-e BL--- 2450 0.235 540 32,500 3.32 1.02 2550 {gagg 25750.270 430 30,000 103 3.20 1.07 .95 2550 .45#alloy 1---- 2055 0.278 45030,500 197 3.30 1.92 .78 2750 .0053 Fest... 2350 0.232 340 32,000 1303.25 1.30 2750 2405 0.247 390 34,500 191 3.21 1.39 .94 2750 2555 0.201435 38,500 207 3.17 1.83 1.02 3000 i. l 2340 0.210 330 32,000 3.10 1.933000 2510 0.225 350 35,500 200 3.17 1.37 .91 3000 .45#alloy,1 2015 0.234350 40,500 210 3.15 1.39 1.00

Average physical properties of cast irons inoculated with ferrosilicon,alloy 2 and al 1011 3 Max. Trans. Trans Resili- Emu Bar No. temp. Ladleaddition load dteiillggwoe T. 8 hard- T. C. Si Cu F. Pounds InchesIn.-lba. Lila/in. Pd. Pct. Pet. 10 2550 .0454 Fe BL--- 2450 275 43032,500 187 3.29 1.84 11 2550 .454 alloy 2---. 2620 0. 278 460 38, 500200 3.28 1. 83 76 12. 2550 .451? alloy 3---- 2810 0. 291 510 39,000 m63. 24 1. 91 1.07

2750 .0454 Fe 81.... 2320 0.240 360 33,000 191 3.31 1.80 2750 45# alloy2.--- 2621 0. 279 460 37, 590 204 3. 24 1.84 90 2750 45# alloy 3----2670 0:292 490 38, 000 206 3. 24 1.86 .88 3000 .0454 Fe 81.... 25000.232 380 32, 500 197 3. 17 1.80 3000 .45# alloy 2---- 2610 0. 242 43039,5) 214 3. 16 1. 80 91 3000 45# alloy 3-..- 2740 0. 277 600 41,000 2133. 14 1. 76 76 Average physical properties of cast irons inoculatedwith. ferrosilicon, alloy 3 and alloy 4 Trans. Brinell Max. Trans.Resili- Bar No. temp Ladle addition load doggeenoe T. S. hlaersg- T. CSi Cu Pounds Inches I'm-lbs. Lba/in. Pct. Pct. Pd. .0455! Fe 51.... 24800. 308 620 34, 500 181 3.25 1. 94 .02 .45# alloy 3.... 2685 0.298 52036,000 200 3.23 1.92 .83 45;! alloy 4...- ,2620 0. 272 460 38, 000 205.3. 23 1. 94 77 0451! Fe 81.... 2360 0. 239 370 33, 500 193 3. 23 1. 9102 .45#a1loy 3.... 2720 0.292 500 38,000 202 3.22 1.84- .84 45# alloy4.-.- 2740 0. 282 490 37, 500 201' 3. 21 1. 89 76 .045# Fe 81.... 23650.242 v 370 35, 500 189 3.22 2. 03 .02 45# alloy 3.... 2630 0. 271 46537, 500 207 3. 20 1. 96 93 .45# alloy 4.-.. 2600 0.204 440 37,000 2073.22 1.94 .65

cast irons inoculated with ferrosilicon and varying amou nts of alloy 3Trans Brinell Max. Trans. Reslli- Bar No. temp Ladle addition loaddailieenee '1. S. liaergds T. 0 Si Cu F. Pounds Inches I'm-lbs. .Lba/in!Pd. Pd. Pct. 3000 2190 0. 240 350 29, 000 v 179 3. 26 1. 81 3000 2420 0.334 540 30, 500 170 3. 21 2. 32 3000 2680 0. 317 570 36, 000 197 3.25 1. 93 3000 N one.... 2330 0. 231 356 30, 000 183 3. 24 1. 92 3000 25#Fe 2260 0. 331 500 30, 500 167 3. 17 2. 49 3000 60;? alloy 3.... 2520 0.281 465 34, 500 199 3. 24 2. 3000 None 2330 0. 296 310 32, 000 194 3. 1.84 3000 Fe Si. 2250 0. 322 490 32, 000 172 3. 18 2. 37 3000 80# alloy3.... 2740 0. 304 550 40, 500 210 3. 17 1. 98 1. 20

Based on the above data alone, it is obvious that thealuminum-silicon-copper alloys and the aluminum-silicon-manganese-copperalloys have I a :beneficial efiect on cast iron. The increase in valuefor deflection shows that these alloys inhibit the formation ofdendritic graphite in cast iron. It will also be apparent that thesealloys do not introduce any weakening or detrimental elements such asare introduced by the addition of ferrosilicon in sufiicient quantitiesto yield comparable deoxidizing effects, the degree of deoxldizing"being indicated by the value for deflection, with low deflection usuallyindicating dendritic graphite.

That the dendritic graphite was inhibited by the use of'my alloys wasverified by examination of the fractures of the bars'which were a cleanbright gray characteristic of normal cast iron, instead of being darkand sooty as characteristic of modified cast iron.

Due to the low melting point of my alloys, no dlfficulty was encounteredin adding them to molten cast iron, even to small ladles at lowtemperatures. The optimum or economical amount of these alloys to beadded appears to be 1%. The best of those alloys studied were thosecontaining 6% aluminum.

In view of the above and other published and unpublished informationconcerning the phenomenon of modified cast iron, it is believed that myalloys serve as a deoxidizing agent for cast iron which is superior topreviously known deoxidlzing agents and which impart to the cast ironbenefits other than those due to deoxidizing alone. It is low in costand is easily added to and readily absorbed by the molten cast ironwithout introducing any weakening or detrimental effects or foundrydefects such as blow holes and in excess of 50 per cent, the balancebeing substantially all iron but not exceeding 30 per cent.

2. A material for addition to molten iron, which will be gray iron whencast, for the purpose of inhibiting or decreasing modification of thecast iron comprising a copper base alloy consisting of 1 to 10 per centaluminum, 6 to 25 per cent silicon, manganese in effective amounts up to25 per cent and copper in excess of 50 per cent. the balance beingsubstantially all iron :but not exceeding 30 per cent.

THOMAS E. BARLOW.

